Polymer conjugates

ABSTRACT

The present invention relates to conjugates of biologically active compounds, preferably therapeutically active compounds, with polymeric moieties having low polydispersity, as well as controlled polymerisation processes for producing the conjugates. An initiation for a controlled radical polymerisation process comprises a biologically active, usually therapeutically active, moiety and the monomer includes zwitterionic monomer for instance 2-methacryloyloxyethyl -2′-trimethylammonium ethyl phosphate inner salt. The process allows close control of the molecular weight and polydispersity of the polymeric moiety and the possibility of optimizing the delivery characteristics of the active agent.

The present invention relates to conjugates of biologically activecompounds, preferably therapeutically active compounds, with polymericmoieties having low polydispersity, as well as controlled polymerisationprocesses for producing the conjugates.

The field of polymer therapeutics involves provision of conjugates oftherapeutically active compounds and polymers of various types.Selection of the class of polymer, and its properties, allows control ofdelivery of the therapeutic to a target within the body of the patientto be treated. Targeting may be active, by providing the conjugate witha specific label, capable of binding to complementary molecules in thetarget region, or passive, by controlling the molecular weight of thepolymer. Conjugation of a therapeutically active compound to a polymermay control the solubility of the therapeutically active compound, itsstability in the circulation, its rate of is removal by the kidneysand/or liver, as well as its immunogenicity.

One example of a polymer therapeutic is the compound PK-1, a conjugateof doxorubicin with hydroxypropylmethacrylamide copolymer. The drug isconjugated to side chains on the polymer by an oligopeptidyl linker.

In WO-A-01118080, controlled radical polymerisation processes are usedto form the polymers from monomers having reactive groups, which may,after polymerisation, be used to conjugate to therapeutic ligands. Thelow polydispersity polymers formed by the controlled radicalpolymerisation processes are said to have particular advantages fortherapeutic use.

Non-polymeric groups may also be conjugated to biologically activemolecules, for instance therapeutically active molecules, to increasetheir water solubility, as well as control their stability inserum/circulation, especially for controlling drug delivery for orallyadministered compounds. In WO-A-9843676, U.S. Pat. No. 5,888,990 andU.S. Pat. No. 6,127,349, a variety of therapeutically active compounds,including compounds which are water-insoluble, are conjugated tozwitterionic groups, to control their solubility or stability in serum.The zwitterionic groups may be phosphocholine groups. The syntheticmethod for conjugating the phosphocholine groups generally involvesreaction of an alcohol with 2-chloro-2-oxo-1,3,2-dioxaphospholane,followed by a ring opening amination with trimethylamine. Otherreactions involve conjugation of an alcohol having a PC group, with thecarboxylic group of a therapeutically active using a carbodiimide toform an ester conjugate.

In our earlier publication WO-A-9315775, ethylenically unsaturatedmonomers including zwitterionic groups, for instance2-methacryloyloxy-2′-ethyltrimethylammoniumphosphate inner salt (MPC),are polymerised by a graft polymerisation process onto carbohydratesubstrates. The substrate may be soluble, for instance a water solublecellulose derivative. Polymerisation involves generation of a freeradical at a hydroxyl group on the substrate by contact with cerium IVions. The zwitterionic treated compounds were then used at surfaces ofmembranes to improve haemocompatibility.

In our earlier application, not published at the priority date hereof,PCT/GB01/04432, atom transfer radical polymerisation is carried outusing monomers including zwitterionic monomers, for instance MPC. Theproduct polymers may be used as matrices for drug delivery, for instanceblock copolymers may form micelles, useful as drug delivery vehicles.There is no suggestion that covalent conjugation of the drug molecule tothe polymer should be considered.

Haddleton, in a paper presented at a meeting of the Society ChemicalIndustry London 1999, describes atom transfer radical polymerisationusing initiators comprising biologically active molecules includingcarbohydrates, especially ribose moieties of nucleosides or steroids.The monomers are ethylenically unsaturated monomers which may form watersoluble products. The monomers may include polyethylene glycol moieties(polyethyleneglycol methacrylate), as well as cationic groups, such asacrylic ester compounds having amine substituents in the alkyl groups.Suitable initiators are formed by acylating an alcohol derivative of thebiologically active molecule with a reactive acid compound having anαhalogen substituent, preferably at a tertiary carbon atom.

The present invention provides polymerisation process in whichethylenically unsaturated monomers including a zwitterionic monomer ofthe general formula IYBX  Iin which Y is an ethylenically unsaturated group selected fromH₂C═CR—CO-A-, H₂C═CR—C₆H₄-A¹-, H₂C═CR—CH₂A², R²O—CO—CR═CR—CO—O,RCH═CH—CO—O—, RCH═C(COOR²)CH₂—CO—O,

A is —O— or NR¹;

A¹ is selected from a bond, (CH₂)_(n)A² and (CH₂), SO₃— in which n is 1to 12;

A² is selected from a bond, —O—, O—CO—, CO—O, CO—NR¹—, —NR¹—CO,O—CO—NR¹—, NR¹—CO—;

R is hydrogen or C₁₋₄alkyl;

R¹ is hydrogen, C₁₋₁alkyl or BX;

R² is hydrogen or C₁₋₄alkyl;

B is a bond, or a straight branched alkanediyl, alkylene oxaalkylene, oralkylene (oligooxalkylene) group, optionally containing one or morefluorine substituents;

X is a zwitterionic group

are polymerised by a living radical polymerisation process in thepresence of an initiator, and a catalyst;

in which the initiator comprises a biologically active moiety and aradical forming moiety.

The initiator may be any compound which has a suitable radical formingmoiety, which may be a moiety from which a halogen atom is removed, orfrom which a radical group is removed, for instance NO-containinggroups, to leave a radical at which polymerisation of the ethylenicallyunsaturated monomers may initiate and propagate. The radical formingmoiety may comprise a halogen atom, preferably attached to a secondaryor, more preferably, tertiary carbon atom, in turn joined to electronwithdrawing groups such as carbonyl, sulphonyl, phosphoryl or arylgroup. A halogen atom is preferably bromine but may alternatively bechlorine or iodine.

Preferably the radical initiator is of the general formula VR¹¹R¹²R¹³C—Y¹  Vwhere:

Y¹is selected from the group consisting of Cl, Br, I, OR¹⁰, SR¹⁴, SeR¹⁴,OP(═O)R¹⁴, OP(═O)(OR¹⁴)₂, O—N(R¹⁴)₂ and S—C(═S)N(R¹⁴)₂, where R¹⁰isalkyl of from 1 to 20 carbon atoms in which each of the hydrogen atomsmay be independently replaced by halide, R¹⁴ is aryl or a straight orbranched C₁-C₂₀ alkyl group, and where an N(R¹⁴)₂ group is present, thetwo R¹⁴ groups may be joined to form a 5- or 6-membered heterocyclicring;

R¹¹ and R¹² are each independently selected from the group consisting ofH, halogen, C₁-C₂₀ alkyl, C₃-C₈ cycloalkyl, C(═O)R¹⁵, C(═O)NR¹⁶R¹⁷,COCl, OH, CN, C₂-C₂₀ alkenyl, oiranyl, glycidyl, aryl, heterocyclyl,aralkyl and aralkenyl, in any of which the alkyl, alkenyl or aryl,heterocyclyl or cycloalkyl groups there may be from 1 to 3 substituentsselected from the group consisting of hydrogen, hydroxy C₁-C₄ alkoxy,acyloxy, aryl, heterocyclyl, C(═O)R¹⁵, C(═O)NR¹⁶R¹⁷, CR¹²R¹³Y¹,CR¹¹R¹²Y¹,oxiranyl and glycidyl;

where R¹⁵ is alkyl of from 1 to 20 carbon atoms, alkoxy of from 1 to 20carbon atoms, oligo(alkoxy) in which each alkoxy group has 1 to 3 carbonatoms, aryloxy or heterocyclyloxy any of which groups may havesubstituents selected from optionally substituted alkoxy, oligoalkoxy,amino (including mono- and di-alkyl amino and trialkyl ammonium, whichalkyl groups, in turn may have substiuents selected from acyl, acyloxy,alkoxy, alkoxycarbonyl, alkenoxycarbonyl, aryl and hydroxy), andhydroxyl groups;

R¹⁶ and R¹⁷ are independently H or alkyl of from 1 to 20 carbon atomswhich alkyl groups, in turn may have substiuents selected from alkoxy,acyl, acyloxy, alkoxycarbonyl, alkenoxycarbonyl, aryl and hydroxy, orR¹⁶ and R¹⁷ may be joined together to form an alkanediyl group of from 2to 5 carbon atoms, thus forming a 3- to 6-membered ring; and

R¹³ is selected from the group consisting of biologically activegroup-substituted alkyl, cycloalkyl, —COR¹⁵, —CONR¹⁶R¹⁷, alkenyl, aryl,heterocyclyl, aralkyl and aralkenyl groups, in any of which the alkyl,alkenyl, aryl, heterocyclyl or cycloalkyl groups may have from 1 to 3substituents selected from the group consisting of hydrogen, hydroxy,C₁-C₄ alkoxy, acyloxy, aryl, heterocyclyl, C(═O)R¹⁵, C(═O)NR¹⁶R¹⁷,—CR¹²R¹³Y¹, CR¹¹R¹²Y¹, oxiranyl and glycidyl where R¹⁵, R¹⁶ and R¹⁷ aregroups as defined above for R¹¹ and R¹² with the biologically activegroup substituted on an alkyl, cycloalkyl, alkenyl, aryl or heterocyclylgroup.

At least one of the groups R¹¹, R¹² and R¹³ should be electronwithdrawing, to stabilise the radical formed upon removal of Y. Suitableelectron-withdrawing groups are mentioned above. Preferably one of R¹¹,R¹² and R¹³, usually R¹³, comprises the electron-withdrawing group. Morepreferably R¹³ is an aryl group or is a group COR¹⁵ in which R¹⁵ isalkoxy. Preferably one of R¹¹ and R¹² is H and the other is methyl.

Since any of R¹¹, R¹² and R¹³ may comprise a substituent CR¹²R¹³ orCR¹¹R¹²Y¹,the initiator may be di-, oligo- or poly- functional.Preferably it is a mono-functional initiator.

The biologically active moiety is preferably a pharmacologically ordiagnostically active moiety, i.e. the pharmacological or diagnosticactivity may be evident in the polymerised product or after cleavage ofthe or part of the polymeric component of the product in vivo, afteradministration. It may be derived from an alcohol, amine, carboxylicacid or other functional (derivatisable) compound which is biologicallyactive (the base compound).

Most preferably the initiator is a compound of general formula VI

where R⁴¹ and R⁴² are independently selected from hydrogen, straight,branched and cyclic alkyl, aryl, aralkyl, hydroxy-alkyl andacyloxyalkyl.

R⁴³ is a biologically active moiety;

Y is a radical forming group or a halogen atom.

Preferably R⁴¹ and R⁴² are not both hydrogen, more preferably each ismethyl, or one is hydrogen and one is methyl.

R⁴³ is preferably derived from a pharmaceutically or diagnosticallyactive alcohol R⁴³OH, for instance in which R⁴³OH is a carbohydrate suchas a sugar.

Another example of a group R⁴³ is a group R⁴⁴AL- derived from R⁴⁴ALOH inwhich groups R⁴⁴ is derived from a pharmaceutically or diagnosticallyactive compound R⁴⁴AH where A is a divalent moiety selected from thegroup consisting of O, NR⁴⁵ (R⁴⁵ is H or lower alkyl), COO and CONR⁴⁵,and L is a divalent linker. L may be an oligopeptide based linker.

Preferably X is an ammonium, phosphonium, or sulphonium phosphate orphosphonate ester zwitterionic group, more preferably a group of thegeneral formula II

in which the moieties A³ and A⁴ ₃ which are the same or different, are—O—, —S—, —NH— or a valence bond, preferably —O—, and W⁺ is a groupcomprising an ammonium, phosphonium or sulphonium cationic group and agroup linking the anionic and cationic moieties which is preferably aC₁₋₁₂-alkanediyl group,

preferably in which W⁺ is a group of formula —W¹—N⁺R³ ₃, —W¹—P+R⁴ ₃ ,—W¹—S⁺R⁴ ₂ or —W¹-Het⁺ in which:

W¹ is alkanediyl of 1 or more, preferably 2-6 carbon atoms optionallycontaining one or more ethylenically unsaturated double or triple bonds,disubstituted-aryl(arylene), alkylene arylene, arylene alkylene, oralkylene aryl alkylene, cycloalkanediyl, alkylene cycloalkyl, cycloalkylalkylene or alkylene cycloalkyl alkylene, which group W¹ optionallycontains one or more fluorine substituents and/or one or more functionalgroups; and

either the groups R³ are the same or different and each is hydrogen oralkyl of 1 to 4 carbon atoms, preferably methyl, or aryl, such asphenyl, or two of the groups R³ together with the nitrogen atom to whichthey are attached form an aliphatic heterocyclic ring containing from 5to 7 atoms, or the three groups R³ together with the nitrogen atom towhich they are attached form a fused ring structure containing from 5 to7 atoms in each ring, and optionally one or more of the groups R³ issubstituted by a hydrophilic functional group; and

the groups R⁴ are the same or different and each is R³ or a group OR³,where R³ is as defined above; or

Het is an aromatic nitrogen-, phosphorus- or sulphur-, preferablynitrogen-, containing ring, for example pyridine.

Monomers in which X is of the general formula in which W+is W¹N^(⊕)R³ ₃may be made as described in our earlier specification WO-A-9301221.Phosphonium and sulphonium analogues are described in WO-A-9520407 andWO-A-9416749.

Generally a group of the formula II has the preferred general formulaIII

where the groups R⁵ are the same or different and each is hydrogen orC₁₋₄ alkyl, and m is from 1 to 4, in which preferably the groups R⁵ arethe same preferably methyl.

In phosphobetaine based groups, X may have the general formula IV

in which A⁵ is a valence bond, —O—, —S— or —NH—, preferably —O—;

R⁶ is a valence bond (together with A⁵) or alkanediyl, —C(O)alkylene- or—C(O)NH alkylene preferably alkanediyl, and preferably containing from 1to 6 carbon atoms in the alkanediyl chain;

W² is S, PR⁷ or NR⁷;

the or each group R⁷′ is hydrogen or alkyl of 1 to 4 carbon atoms or thetwo groups R⁷ together with the heteroatom to which they are attachedform a heterocyclic ring of 5 to 7 atoms;

R⁸ is alkanediyl of 1 to 20, preferably 1 to 10, more preferably 1 to 6carbon atoms;

A⁶ is a bond, NH, S or O, preferably O; and

R⁹ is a hydroxyl, C₁₋₁₂ alkyl, C₁₋₁₂ alkoxy, C₇₋₁₈ aralkyl,C₇₋₁₈-aralkoxy, C₆₋₁₈ aryl or C₆₋₁₈ aryloxy group.

Monomers comprising a group of the general formula IV may be made bymethods as described in JP-B-03-031718, in which an amino substitutedmonomer is reacted with a phospholane.

In compounds comprising a group of the general formula IV, it ispreferred that

A⁵ is a bond;

R⁸ is a C₂₋₆ alkanediyl;

W² is NR⁷:

each R⁷ is C₁₋₄ alkyl;

R⁸ is C₂₋₆ alkanediyl;

A⁶ is O; and

R⁹ is C₁₋₄ alkoxy.

Alternatively X may be a zwitterion in which the anion comprises asulphate, sulphonate or carboxylate group.

One example of such a group is a sulphobetaine group, of the generalformula XI

where the groups R³⁶ are the same or different and each is hydrogen orC₁₋₄ alkyl and s is from 2 to 4.

Preferably the groups R³⁶ are the same. It is also preferable that atleast one of the groups R³⁶ is methyl, and more preferable that thegroups R³⁶ are both methyl.

Preferably s is 2 or 3, more preferably 3.

Another example of a zwitterionic group having a carboxylate group is anamino acid moiety in which the alpha carbon atom (to which an aminegroup and the carboxylic acid group are attached) is joined through alinker group to the backbone of the biocompatible polymer. Such groupsmay be represented by the general formula XII

in which A⁷ is a valence bond, —O—, —S— or —NH—, preferably —O—,

R³⁷ is a valence bond (optionally together with A⁷) or alkanediyl,—C(O)alkylene- or —C(O)NHalkylene, preferably alkanediyl and preferablycontaining from 1 to 6 carbon atoms; and

the groups R³⁸ are the same or different and each is hydrogen or alkylof 1 to 4 carbon atoms, preferably methyl, or two or three of the groupsR³⁶, together with the nitrogen to which they are attached, form aheterocyclic ring of from 5 to 7 atoms, or the three group R³⁸ togetherwith the nitrogen atom to which they are attached form a fused ringheterocyclic structure containing from 5 to 7 atoms in each ring.

Another example of a zwitterion having a carboxylate group is a carboxybetaine —N^(⊕)(R³⁹)₂(CH₂)_(r)COO^(⊖) in which the R³⁹ groups are thesame or different and each is hydrogen or R₁₋₄ alkyl and r is 2 to 6,preferably 2 or 3.

In the zwitterionic monomer of the general formula I it is preferredthat the ethylenic unsaturated group Y is H₂C═CR—CO-A-. Such acrylicmoieties are preferably methacrylic, that is in which R is methyl, oracrylic, in which R is hydrogen. Whilst the compounds may be(meth)acrylamido compounds (in which A is NR¹), in which case R¹ ispreferably hydrogen, or less preferably, methyl, most preferably thecompounds are esters, that is in which A is O.

In monomers of the general formula I, especially where Y is thepreferred (alk)acrylic group, B is most preferably an alkanediyl group.Whilst some of the hydrogen atoms of such group may be substituted byfluorine atoms, preferably B is an unsubstituted alkanediyl group, mostpreferably a straight chain group having 2 to 6 carbon atoms.

A particularly preferred zwitterionic monomer is2-methacryloyloxyethyl-2′-trimethylammonium ethyl phosphate inner salt.

In the polymerisation process, the ethylenically unsaturated monomersmay further include a comonomer. Comonomers are copolymerisable with thezwitterionic monomer and are preferably selected from anionic, cationicand nonionic monomers. It is generally preferred that the monomermixture include at least one nonionic monomer. Another class ofcomonomer is a cross-linking monomer having a functional group which maybe cured after polymerisation to cross-link the polymer.

Examples of suitable comonomers are compounds of the general formula X

in which R³′ is selected from hydrogen, halogen, C₁₋₄alkyl and groupsCOOR² in which R² is hydrogen and C₁₋₄ alkyl;

R³² is selected from hydrogen, halogen and C₁₋₄ alkyl;

R³³ is selected from hydrogen, halogen, C₁₋₄ alkyl and groups COOR²provided that R³′ and R³³ are not both COOR²; and

R³⁴ is a C₁₋₁₀ alkyl, a C₁₋₂₀ alkoxycarbonyl, a mono-or di-(C₁₋₂₀ alkyl)amino carbonyl, a C₆₋₂₀ aryl (including alkaryl) a C₇₋₂₀ aralkyl, aC₆₋₂₀ aryloxycarbonyl, a C₁₋₂₀-aralkyloxycarbonyl, a C₆₋₂₀ arylaminocarbonyl, a C₇₋₂₀ aralkyl-amino, a hydroxyl or a C₂₋₁₀ acyloxy group,any of which may have one or more substituents selected from halogenatoms, alkoxy, oligo-alkoxy, aryloxy, acyloxy, acylamino, amine(including mono and di-alkyl amino and trialkylammonium in which thealkyl groups may be substituted), carboxyl, sulphonyl, phosphoryl,phosphino, (including mono- and di- alkyl phosphine andtri-alkylphosphonium), zwitterionic, hydroxyl groups, vinyloxycarbonyland other vinylic or allylic substituents, and reactive silyl orsilyloxy groups, such as trialkoxysilyl groups;

or R³⁴ and R³³ or R³⁴ and R³² may together form —CONR³⁵CO in which R³⁵is a C₁₋₂₀ alkyl group.

It is preferred for at least two of the groups R³¹R³²R³³ and R³⁴ to behalogen or, more preferably, hydrogen atoms. Preferably R³¹ and R³² areboth hydrogen atoms. It is particularly preferred that compound ofgeneral formula X be a styrene-based or acrylic based compound. Instyrene based compounds R³⁴ represents an aryl group, especially asubstituted aryl group in which the substituent is an amino alkyl group,a carboxylate or a sulphonate group. Where the comonomer is an acrylictype compound, R³⁴ is an alkoxycarbonyl, an alkyl amino carbonyl, or anaryloxy carbonyl group. Most preferably in such compounds R³⁴ is aC₁₋₂₀-alkoxy carbonyl group, optionally having a hydroxy substituent.Acrylic compounds are generally methacrylic in which case R³³ is methyl.

Where a comonomer is included in the polymerisation process of theinvention, the molar ratio of zwitterionic monomer to comonomer ispreferably in the range 1:50 to 50:1, more preferably in the range 1:10to 10:1, more preferably in the range 1:5 to 1:1.

In the atom or group radical transfer polymerisation process thetransition metal compound which comprises a component of the catalyst isM_(t) ^(n+)X′_(n), where:

M_(t) ^(n+) may be selected from the group consisting of Cu¹⁺, Cu²⁺,Fe²⁺, Fe³⁺, Ru²⁺, Ru³⁺, Cr²⁺, Cr³⁺, Mo²⁺, Mo³⁻, W²⁺, W³⁺, Mn²⁺, Mn³⁺,Mn⁴⁺, Rh³⁺, Rh⁴⁺, Re²⁺, Re³⁺, Co⁺, Co²⁺, Co³⁺, V²⁺, V³⁺, Zn⁺, Zn²⁺,Ni²⁺, Ni³⁺, Au⁺, AU²⁺ Ag⁺ and Ag²⁺;

X′ is selected from the group consisting of halogen, C₁-C₆-alkoxy,(SO₄)_(1/2), (PO₄)_(1/3), (R¹⁸ ₂PO₄)½(R¹⁸ ₂PO₄), triflate,hexafluorophosphate, methanesulphonate, arylsulphonate, CN and R¹⁹CO₂,where R¹⁸ is aryl or a straight or branched C₁₋₂₀alkyl and R¹⁹ is H or astraight or branched C₁-C₆ alkyl group which may be substituted from 1to 5 times with a halogen; and

n is the formal charge on the metal (O≦n≦7).

Preferably X′ is halide, most preferably chloride or bromide.Particularly suitable transition metal compounds are based on copper orruthenium, for instance CuCl or RuCl₂.

In the catalyst, the ligand is preferably selected from the groupconsisting of:

a) compounds of the formulas:R²⁰—Z—R²¹ andR²⁰—Z—(R²²—Z)_(m)R²¹where:

R²⁰ and R²¹ are independently selected from the group consisting of H,C₁-C₂₀ alkyl, aryl, heterocyclyl and C₁-C₆ alkoxy, C₁-C₄ dialkylamino,C(═O)R²², C(═O)R²³R²⁴ and A⁷C(═O)R²⁵, where A⁷ may be NR²⁶ or O; R²² isalkyl of from 1 to 20 carbon atoms, aryloxy or heterocyclyloxy; R²³ andR²⁴ are independently H or alkyl of from 1 to 20 carbon atoms or R²³ andR²⁴ may be joined together to form an alkanediyl group of from 2 to 5carbon atoms, thus forming a 3- to 6-membered ring; R²⁵ is H, straightor branched C₁-C₂₀ alkyl or aryl and R²⁶ is hydrogen, straight orbranched; C₁₋₂₀-alkyl or aryl; or R²⁰ and R²¹ may be joined to form,together with Z, a saturated or unsaturated ring;

Z is O, S, NR²⁷ or PR²⁷, where R²⁷ is selected from the same group asR²⁰ and R²¹, and where Z is PR²⁷, R²⁷ can also C₁-C₂₀ alkoxy or Z may bea bond, CH₂ or a fused ring, where one or both of R²⁰ and R²¹ isheterocyclyl,

each R²² is independently a divalent group selected from the groupconsisting of C₁-C₈ cycloalkanediyl, C₁-C₈ cycloalkanediyl, arenediyland heterocyclylene where the covalent bonds to each Z are at vicinalpositions or R²² may be joined to one or both of R²⁰ and R²¹ toformulate a heterocyclic ring system; and

m is from 1 to 6;

b) CO;

c) porphyrins and porphycenes, which may be substituted with from 1 to 6halogen atoms, C₁₋₆ alkyl groups, C₁₋₆-alkoxy groups,C₁₋₆alkoxycarbonyl, aryl groups, heterocyclyl groups, and C₁₋₄ alkylgroups further substituted with from 1 to 3 halogens;

d) compounds of the formula R²³R²⁴C(C(═O)R²⁵)₂, where R^(25 is)C₁₋₂₀alkyl, C₁₋₂₀ alkoxy, aryloxy or heterocyclyloxy; and each of R²³ and R²⁴is independently selected from the group consisting of H, halogen, C₁₋₂₀alkyl, aryl and heterocyclyl, and R²³ and R²⁴ may be joined to form aC₁₋₈, cycloalkyl ring or a hydrogenated aromatic or heterocyclic ring,of which the ring atoms may be further substituted with 1 to 5 C₁₋₆alkyl groups, C₁₋₆ alkoxy groups, halogen atoms, aryl groups, orcombinations thereof; and

e) arenes and cyclopentadienyl ligands, where said cyclopentadienylligand may be substituted with from one to five methyl groups, or may belinked through and ethylene or propylene chain to a secondcyclopentadienyl ligand.

Selection of a suitable ligand is, for instance, based upon thesolubility characteristics and/or the separability of the catalyst fromthe product polymer mixture. Generally it is catalyst to be soluble in aliquid reaction mixture, although under some circumstances it may bepossible to immobilise the catalyst, for instance an a porous substrate.For the preferred process, which is carried out in the liquid phase, theligand is soluble in a liquid phase. The ligand is generally a nitrogencontaining ligand. The preferred ligand may be a compound including apyridyl group and an imino moiety, such as bipyridine, or

where R⁴⁰ is a suitable alkyl group, the substituent being variable andadaptable to confer desired solubility characteristics or may betriphenylphosphine or 1,1,4,7,10,10-hexamethyl-triethylene tetramine.

Such nitrogen-containing ligands are usefully used in combination withcopper (I) chloride, copper (I) bromide or ruthenium chloride transitionmetal compounds as part of the catalyst.

The living radical polymerisation process of the invention is preferablycarried out to achieve a degree of polymerisation in the range 2 to 100.Preferably the degree of polymerisation is in the range 5 to 50, morepreferably in the range 10 to 25. In the preferred group or atomtransfer radical polymerisation technique, the degree of polymerisationis directly related to the initial ratios of initiator to monomer.Preferably the ratio is in the range 1:(2 to 100), more preferably inthe range of 1:(5 to 50), most preferably in the range 1:(10 to 25).

The ratio of metal compound and ligand in the catalyst should beapproximately stoichiometric, based on the ratios of the components whenthe metal ion is fully complexed. The ratio should preferably be in therange 1:(0.5 to 2) more preferably in the range 1:(0.8:1.25). Preferablythe range is about 1:1.

In the process, the catalyst may be used in amounts such that a molarequivalent quantity as compared to the level of initiator is present.However, since catalyst is not consumed in the reaction, it is generallynot essential to include levels of catalyst as high as of initiator. Theratio of catalyst (based on transition metal compound) to initiator ispreferably in the range 1:(1 to 50), more preferably in the range 1:(1to 10).

Whilst the polymerisation reaction may be carried out in the gaseousphase, it is more preferably carried out in the liquid phase. Thereaction may be heterogeneous, that is comprising a solid and a liquidphase, but is more preferably homogeneous. Preferably the polymerisationis carried out in a single liquid phase. Where the monomer is liquid, itis sometimes unnecessary to include a non-polymerisable solvent. Moreoften, however, the polymerisation takes place in the presence of anon-polymerisable solvent. The solvent should be selected having regardto the nature of the zwitterionic monomer and any comonomer, forinstance for its suitability for providing a common solution containingboth monomers. The solvent may comprise a single compound or a mixtureof compounds.

Where the zwitterionic monomer is MPC, may be desirable to include waterin the polymerisation mixture. Preferably water should be present in anamount in the range 10 to 100% by weight based on the weight ofethylenically unsaturated monomer. Preferably the totalnon-polymerisable solvent comprised 1 to 500% by weight based on theweight of ethylenically unsaturated monomer. It has been found that thezwitterionic monomer and water should be in contact with each other foras short a period as possible prior to contact with the initiator andcatalyst. It may be desirable therefore for all the components of thepolymerisation other than the zwitterionic monomer to be premixed andfor the zwitterionic monomer to be added to the premix as the lastadditive.

It is often desired to copolymerise MPC or other zwitterionic monomerwith a comonomer and/or an initiator which is insoluble in water. Insuch circumstances, a solvent or co-solvent (in conjunction with water)is included to confer solubility on both MPC and the more hydrophobicmonomer. Suitable organic solvents are ethers, esters and, mostpreferably, alcohols. Especially where a mixture of organic solvent andwater is to used, suitable alcohols are C₁₋₄-alkanols. Methanol isexpected to be particularly suitable in the polymerisation process ofthe invention. Ethanol and isopropanol are likely to be useful also.

The process may be carried out at raised temperature, for instance up to60 to 80° C. The process may proceed sufficiently fast at ambienttemperature.

The polymerisation process of the invention should preferably be carriedout so as to provide polymers of zwitterionic monomers having apolydispersity (of molecular weight) of less than 1.5, as judged by gelpermeation chromatography. Polydispersities in the range 1.2 to 1.4 areis preferred. Conversion rates achieved in the process should be as highas possible, for instance over 90% often over 95% or higher. It ispreferred that the process be continued until a conversion level of atleast 50%, or usually, at least 70% is reached.

According to a further aspect of the invention there is provided a novelcompound comprising a conjugate of a biologically active moiety and apolymer group having a general formula VII:

in which M¹ is the divalent group formed when the compound of thegeneral formula I as defined in claim 1 is polymerised, M² is thedivalent group formed when a comonomer as defined in claim 18 ispolymerised, and I¹ is the residue of the initiator defined in claim 1which comprises said biologically active moiety, and R³⁶ is amonofunctional group or atom which terminates the polymeric group -M¹_(n)M² _(m)-, n is at least 2 and m is at least 0.

Preferably the degree of polymerisation of monomers forming residues M¹is at least 5, more preferably at least 10, that is n is at least 5,preferably at least 10. The value of n is generally no more than 100,preferably less than 50.

Groups M² are derived from comonomer, for instance of the generalformula X defined above. The groups M² thus have the general formula IX

Where a comonomer is not included, n is 0. In the general formuladefining the polymer, the groups M¹ and M² are randomly arranged. Theratio n:m represents the molar ratio of zwitterionic monomer tocomonomer used in the polymerisation.

R³⁶ may include a further polymeric block, for instance, formed in asecond controlled radical polymerisation step involving a furtherethylenically unsaturated monomer, for instance which may have thegeneral formula X above.

The selection of suitable monomer or monomer mixtures to form such asecond block may allow an amphiphilic polymer to be formed, i.e. if thesecond block is hydrophobic relative to the block

The present invention also covers reverse block copolymers to the typedescribed above, that is where a first block is formed by polymerisationof monomers not including a monomer of the formula I, in the presence ofthe specified initiator, and a second block is formed in a secondcontrolled radical polymerisation of monomer including zwitterionicmonomer in the presence of the product of the first polymerisation step.

The degree of polymerisation and the polydispersity of the polymericgroup of the conjugate of the invention produced by the polymerisationprocess of the first aspect of the invention, allows for control of thesolubility of the biologically active compound. Where the compound istherapeutically active, for instance, control of the nature of thepolymeric group may allow for good control of delivery of thetherapeutic to a target, organ, tumour or cell. The molecular weightshould be high enough to minimise removal of the conjugate by thekidneys, but should be below the threshold which renders a compoundhepatoselective. For instance the weight should be selected so as totake advantage of the phenomenon of enhanced permeability and retention(EPR) observed in solid tumours where the active is an anti-tumour agentfor local delivery to the tumour. It may be desirable to provide theconjugate with an active targeting moiety, for instance by derivatisingterminal groups R³⁶ with a binding moiety, for instance an antigen,antibody, oligopeptide, oligonucleotide, lectin, biotin, or other memberof a specific binding pair, capable of binding to another number of thebinding pair localised at the target organ. The biologically activecompound may be a protein or polypeptide, a carbohydrate, a nucleic acidor another drug, or may comprise a combination of such components.

The polymeric group may further provide improved stability in thecirculation or in serum, or improved circulation times, as has beendescribed for the monomeric PC-ylation in WO-A-9843676 etc. Theinvention is believed to be of particular utility where the compoundfrom which the biologically active compound is derived (e.g. R⁴⁴AH orR⁴³⁰H) has limited water solubility, for instance solubility less thanin the range 0.1 to 10 mg/ml. Preferably the water solubility of theconjugate compound is at least 10 molar times higher, preferably atleast 100 times higher than the base compound.

The present invention also provides specific drug-polymer conjugateshaving increased solubility in water as compared to the base drug andintermediates useful for producing the polymer conjugates in an atomtransfer radical polymerisation method. The intermediates are compoundsof the general formula VI where the group R⁴³ is the residue of aphenylic compound R⁴³⁰H selected from salicylic acid, acetaminophen anddexamethasone. Thus the intermediates are 2-bromo-2-alkyl-alkanoylesters of salicylic acid, acetaminophen and dexamethasone.

The invention is illustrated in the following reaction schemes.

REFERENCE EXAMPLE 1

General Method of Producing Initiators

In the above reaction, L is a leaving group. This may be, for instance,a halogen atom, an acyloxy group (i.e. the acylation reagent is ananhydride), or a group —ON═C(Me)₂. Where the leaving group is the lastmentioned compound the esterification reaction may be conducted indioxane, at raised temperature, for instance 60° C.

The above general reaction is carried out with compounds in which R⁴³OHis a suitably protected carbohydrate, that is one in which all thehydroxyl groups apart from the hydroxyl group desired to be derivatised,are protected with removable groups. Conventional protecting groupchemistry is appropriate. The carbohydrate may be a ribose group of anucleoside. Alternatively R⁴³OH may be an oligosaccharide. In acarbohydrate R⁴³OH or a sugar such as glucose or galactose all otherhydroxyl groups are protected during the reaction, for instance byacetylation or by protection of gem. diols by isopropylidene groups.Alternatively R⁴³OH may be cholesterol.

A specific initiator may be formed by the following reaction scheme:

EXAMPLE 1

Cholesteryl-2-bromoisobutyrate is used as an initiator in an atomtransfer radical polymerisation process using copper (1) bromide and a2-pyridinecarbaldehyde imine ligand, as described in U.S. Pat. No.6,310,149, using MPC monomer to form a polymer having a degree ofpolymerisation between 2 and 50, for instance in the range 5 to 20,using an appropriate molar ratio of initiator to monomer. The solvent isselected to provide common solubility of the initiator and the monomer,and to allow recovery of the polymer, for instance methanol.

An alternative polymerisation uses copper (I) bromide catalyst andbipyridine ligand. The solvent system in this case preferably includeswater, or alcohol, preferably methanol, or a mixture of water andmethanol.

The product may be analysed by gel permeation chromatography, to assessthe number average and weight average molecular weight and thepolydispersity.

EXAMPLE 2

Preparation of Salicylic Acid Bromo-Modified Initiator

A 500 ml round bottom flask, resting in a water bath, with a stirrer barwas charged with 10 g of salicylic acid (Aldrich) and acetonitrile(Romil) was added in sufficient quantity to dissolve. 0.5 equivalent ofN,N,N′,N′-tetramethylethylenediamine (TMEDA, Aldrich) was added. Adropping funnel was charged with approximately 50 ml of acetonitrile and1.25 equivalents of 2-bromoisobutyryl bromide (Aldrich). The contents ofthe flask were added dropwise over 2 hours. The reaction was leftstirring over night and with a balloon fitted to equalise any pressurechange. The amine halide salt precipitate was filtered off and theacetonitrile removed in vacuo. The product was dissolved into 200 ml ofd.i. water and any excess 2-bromoisobutyryl bromide hydrolysed withsodium bicarbonate. The bromo-functionalised drug was extracted from thewater using 150 ml of DCM, which was removed in vacuo to obtain thepurified salicylic acid bromo-modified initiator as an off-white solid.

¹H NMR spectroscopy shows the aromatic protons at δ 8.05 ppm (doublet),δ 7.65 ppm (triplet), δ 7.4 ppm (triplet) and δ 7.15 ppm (doublet)respectively. There is a methyl peak at ca. δ 2 ppm from the methyls onthe bromide group. There is no evidence of the OH proton which would beexpected at δ 10 ppm. This is also supported by the ¹³C NMR, wherecarbon peaks are as follows; COOH— δ 167.5 ppm, ArC—COOH— δ 121 ppm,ArC— δ 135ppm, ArC— δ 133 ppm, ArC— δ 137.5 ppm, ArC— δ 124 ppm, ArCOOR— δ 152 ppm, 3 COOR δ 170 ppm, C(CH₃)₃Br—δ 58 ppm and C(CH₃)₃Br at δ 31ppm where R═C(CH₃)₃Br

EXAMPLE 3

Preparation of 4-Acetamidophenyl Bromo-Modified Initiator

The reaction was carried out according to the procedure outlined inExample 2 but using 4-acetamidophenyl as the drug to be modified. Theproduct was isolated as an off-white solid.

¹H NMR spectroscopy shows aromatic protons at δ 7.6 ppm and δ 7.05 ppm.The methyl peak within the acetamido group appears at δ 1.98 ppm asexpected and the proton on the amide group appears as a very small peakat ca. δ 9.8-9.9 ppm. As expected there is no evidence of the hydroxylproton at δ 9.14 ppm, however there is now a methyl peak at ca. δ 2 ppmfrom the methyls on the bromide group. This is also supported by the ¹³CNMR, where the NH—C═O can be found at δ 170 ppm, C—CO—C at δ 148 ppm,C—CNH—C at δ 138 ppm, C—CNH—Cat δ 123 ppm and their has been a shift forthe C—CO—Cfrom δ 115 ppm to δ 122 ppm, NH—C═O—CH₃ can be found at δ 24ppm. Additionally there are new peaks at δ 31 ppm corresponding to themethyl groups on the bromide molecule. The carbonyl peak in the bromidegroup is also evident at δ 170 ppm and the methyl group, CH₃—CBr—CH₃ canbe found at δ 58 ppm.

EXAMPLE 4

Preparation of Dexamethasone Bromo-Modified Initator

The reaction was carried out according to the procedure outlined inExample 2 but using dexamethasone as the drug to be modified. Theproduct was isolated as a brown gum.

Proton NMR spectra (shown in FIG. 1) showed agreement with standardspectra for dexamethasone with a set of shifts owing to the attachmentof the 2-bromoisobutyryl bromide at one of the OH sites. The protons (a)in the starting material have two peaks at δ 4.0 and δ 4.5 ppm, in FIG.1 these two peaks have shifted to ca. δ 4.68 and ca. δ 5 ppm which wouldsuggest that the initiator group has reacted at the hydroxyl on thismethylene group. In the ¹³C spectra there are also additional peaks notseen in the standard dexamethasone spectra at δ 31 ppm due to the methylcarbons; at δ 59 ppm due to the methyl carbon and at δ 68 due to thecarbonyl carbon; all from the 2-bromoisobutyryl.

EXAMPLE 5

Preparation of Poly(MPC)-Modified Salicylic Acid

A stock solution of HPLC grade methanol was degassed and stored underN₂. A 100 ml 2-necked round bottom flask containing a stirrer bar wasflushed with N₂for 10 minutes, then sealed using 2 rubber septums. Adinitrogen atmosphere was maintained. All glass vials to be used forweighing material were also flushed with N₂ for 5 minutes before sealinguntil used.

TABLE 1 Reactant Amounts for Preparation of Poly(MPC)-modified SalicylicAcid Salicylic Acid-Br MPC (A) BPy CuBr Molar Ratio 13 1   2 1 No ofmols 2.29 × 10⁻² 1.74 × 10⁻³ 4.59 × 10⁻³ 2.3 × 10⁻³ Calculated 6.8 g 0.50.2109 g 0.097 g weight

The salicylic acid bromo-modified initiator (A) (synthesised as inExample 2) was accurately weighed and transferred to the round bottomflask ml of the stock methanol was added using a syringe. An excess of2,2′-bipyridine (Bpy) was weighed into a second vial followed by thecopper (I) bromide. The sealed vial was tapped gently against the sideof the bench to mix the contents then added to the round bottom flask.An excess of MPC was rapidly weighed into a 3^(rd) vial, stirring in theround bottom flask was increased and the MPC added swiftly. Stirring wasreduced to a gentle mixing and the reaction left to proceed for 1½-2hours. The reaction was monitored by NMR by comparing integration of theMPC vinyl peaks at δ 5.6 and 6.1 ppm with the backbone methyl peak,which can be found at δ 1.0 ppm. A % conversion can be calculated fromthe integration value of the polymer peak as follows:

${\%\mspace{14mu}{Conversion}} = {\frac{Z}{Z + 5} \times 100}$(where  Z  is  the  integration  value  of  the  polymer  peak)

The resulting polymer was dissolved in methanol. A chromatography columnfitted with a glass sinter was filled ½ to ¾ full with silica gel (grade7754, 70-230 mesh, Aldrich Chemical Co.) and methanol passed down untilall heat had dissipated from the column, any elution up to this pointwas discarded. The dissolved polymer was passed down the column toremove the (blue) copper and the dissolved polymer solution collected ina 500 ml round bottom flask. The solvent was removed in vacuo and thepolymer dried by freeze-drying to yield greater than 50% of a whitefluffy crystalline solid.

Upon polymerisation the salicylic acid is identifiable in the ¹H NMRspectrum as a series of peaks between δ 6.9 and 8.8 ppm, alongside theexpected poly(MPC) peaks, and also confirms the correct monomer:initatorratio. Aqueous GPC showed the polydispersity to be 1.14.

In the reaction scheme “OPC” is the abbreviation for

EXAMPLE 6

Preparation of Poly(MPC)-Modified 4-Acetamidophenyl

The method for the preparation of Poly(MPC)-modified 4-Acetamidophenylwas exactly that as described in Example 5 using (B) (synthesised as inExample 3) as the initiator and the following quantities of reactants:

TABLE 2 Reactant Amounts for Preparation of Poly(MPC)-modified 4-Acetamidophenol 4Acetamido MPC phenol-Br (B) BPy CuBr Molar Ratio 13 11.447 2.7 No of mols 2.17 × 10⁻² 1.67 × 10⁻³ 3.14 × 10⁻³ 8.02 × 10⁻⁴Calculated weight 6.45 gg 0.5 g 0.49 g 0.115 g

The reaction yielded greater than 50% of a crystalline fluffy whitesolid. Upon polymerisation, the paracetamol is identifiable in the ¹HNMR spectrum as a series of peaks between δ 6.9 and 8.8 ppm, alongsidethe expected poly(MPC) peaks. The ratio of MPC: initiator was asexpected and aqueous GPC gave a polydispersity of 1.07.

EXAMPLE 7

Preparation of Poly(MPC)-Modified Salicylic Acid

The method for the preparation of Poly(MPC)-modified salicylic acid wasexactly that as described in Example 4 using (A) (synthesised in Example3) as the initiator and the following quantities of reactants:

TABLE 3 Reaction Amounts For Preparation of Poly(MPC)-modified SalicylicAcid (1:64) Salicylic MPC Acid-Br BPy CuBr Molar Ratio 64 1 1.447 3.33No of mols 3.36 × 10⁻² 5.23 × 10⁻⁴ 9.74 × 10⁻² 2.02 × 10⁻⁴ Calculated 10g 0.15 g 0.152 g 0.029 g weight

The product was isolated as a white fluffy crystalline solid. NMRconfirmed 100% conversion and the correct monomer: initiator ratio.Aqueous GPC was used to measure polydispersity which was 1.09.

EXAMPLE 8

Preparation of Poly(MPC)-Modified Dexamethasone

The method for the preparation of Poly(MPC)-modified dexamethasone wasexactly that as described in Example 5 using (C) (synthesised as inExample 4) as the initiator and the following quantities of reactants:

TABLE 4 Reactant Amounts for Preparation of Poly(MPC)-modifiedDexamethasone Dexametha- sone-Br MPC (C) BPy CuBr Molar Ratio 10 1 21.44 No of mols 1.85 × 10⁻² 1.85 × 10⁻³ 3.69 × 10⁻³ 1.28 × 10⁻³Calculated 5.49 g 1 g 0.58 g 0.185 g weight

The reaction yielded greater than 50% of a pale yellow solid. 1H NMRconfirmed the expected ratio of monomer:initiator and GPC gave apolydispersity of 1.08.

EXAMPLE 9

Effect of Polymer Modification on Drug Solubility

TABLE 5 shows the effect of the MPC polymer modification on thesolubility of the drug compounds: Solubility Solubility Solubility ofSolubility of of Drug of Drug Polymer-Drug Polymer-Drug Drug (g/ml)(mol/ml) (g/ml) (mol drug/ml) Salicylic Acid 2.2 × 10⁻³ 1.6 ×10⁻⁵ >1.03 >3.3 × 10⁻⁴ (13:1) Salicylic Acid 2.2 × 10⁻³ 1.6 ×10⁻⁵ >0.92 >6.4 × 10⁻⁵ (64:1) Acetamidophen 6.7 × 10⁻³ 4.4 ×10⁻⁵ >0.64 >2.1 × 10⁻⁴

The polymer-modified compound was added step-wise to water to determinethe maximum solubility at room temperature. An upper limiting solubilitywas not determined, as the viscosity for the solution increased isdramatically due to the presence of the polymer making it difficult toassess when no more compound would dissolve. The figures quoted simplydemonstrated that the water solubility of the drug has been increased ona mole-for-mole basis given the increase in molecular weight due to theattachment of the MPC polymer.

EXAMPLE 10.1 Preparation of 4-(3-(2-bromo,2-methyl-propionate)phenyl)-propionic acid N-hydroxysuccinimide ester(prospective)

To a solution of 4-(3-hydroxyphenyl)-propionic acid (a) in acetonitrile,TMEDA (0.55 equiv) is added and stirred at room temperature for about 5min. A solution of 2-bromo, 2-methyl propionic acid bromide (b) (1.5equivalent) in acetonitrile is slowly added. After about 15 min ofaddition a white precipitate should be observed in the reaction vessel.After addition of the acid bromide (about 30 min), the reaction isstirred for about a further 60 min. The reaction mixture is filtered andthe solvent removed in vacuo to yield 4-(3-(2-bromo, 2-methyl-propionicester)phenyl)-propionic acid (c). To a solution of 4-(3-(2-bromo,2-methyl-propionate)phenyl)-propionic acid (1 equivalent) in THF,N-hydroxy succinimide (1.05 equivalents) and dicyclohexylcarbodi-imide(d) (1.05 equivalents) is added at −18° C. and stirred for about 2 h.The reaction is allowed to warm to room temperature and stirred for afurther 10 h. The reaction is worked up as described by Rutinger & Rueggin Biochem J., 133(3), 538, 1973 to yield 4-(3-(2-bromo,2-methyl-propionate)phenyl)-propionic acid N-hydroxysuccinimide ester(e).

Example 10.1—Preparation of 2-bromo, 2-methyl-propionic acidN-hydroxysuccinimide ester.

EXAMPLE 10.2

Lysozyme Conjugation to ATRP Initiator

To a suspension of 4-(3-(2-bromo, 2-methyl-propionate)phenyl)-propionicacid N-hydroxysuccinimide (e) ester in borate buffer, lysozyme is addedand the resulting mixture gently shaken at room temperature for about 8h. The initiator (f) is used without isolation.

Example 10.2—conjugation of initiator to lysozyme.

EXAMPLE 10.3

ATRP Using the Conjugated Initiator

The initiator solution is purged with nitrogen for about 30 min, andthen copper bromide catalyst and the bipyridyl ligand added. Thesolution is further purged with nitrogen, and MPC added (50× catalystconcentration, target Mn 15 000). The green reaction mixture is stirredfor about 8 h at room temperature. The reaction is monitored by NMRaliquots, for consumption of the MPC methacrylate groups. The reactionmixture is analysed and product (g) purified by CapillaryElectrophoresis.

Example 10.3—ATRP using the lysozyme conjugated initiator.

1. A polymerisation process for forming polymer conjugates ofbiologically active compounds in which ethylenically unsaturatedmonomers including a zwitterionic monomer of the general formula IYBX  I in which Y is an ethylenically unsaturated group selected fromH₂C═CR—CO-A-, H₂C═CR—C₆H₄-A¹-, H₂C═CR—CH₂A², R²O—CO—CR═CR—CO—O,RCH═CH—CO—O—, RCH═C(COOR²)CH₂—CO—O,

A is —O— or NR¹; A¹ is selected from the group consisting of a bond,(CH₂)_(n)A² and (CH₂)_(n) SO₃— in which n is 1 to 12; A² is selectedfrom the group consisting of a bond, —O—, O—CO—, CO—O, CO—NR¹—, —NR¹—CO,O—CO—NR¹—, NR¹—CO—O—; R is hydrogen or C₁₋₄ alkyl; R¹ is selected fromthe groups consisting of hydrogen, C₁₋₄ alkyl or BX; R² is hydrogen orC₁₋₄ alkyl; B is selected from the group consisting of a bond, or astraight and branched alkanediyl, alkylene oxaalkylene, and alkylene(oligooxalkylene) groups, optionally containing one or more fluorinesubstituents; and X is a zwitterionic group are polymerised by a livingradical polymerisation process in the presence of an initiator, and acatalyst; in which the initiator is a compound of general formula VR¹¹R¹²R¹³C—Y  V where: Y¹ is selected from the group consisting of Cl,Br, I, OR¹⁰, SR¹⁴, SeR¹⁴, OP(═O)R¹⁴, OP(═O)(OR¹⁴)₂, O—N(R¹⁴)₂ andS—C(═S)N(R¹⁴)₂, where R¹⁰ is alkyl of from 1 to 20 carbon atoms in whicheach of the hydrogen atoms may be independently replaced by halide, R¹⁴is aryl or a straight or branched C₁-C₂₀ alkyl group, and where anN(R¹⁴)₂ group is present, the two R¹⁴ groups may be joined to form a 5-or 6-membered heterocyclic ring; R¹¹ and R¹² are each independentlyselected from the group consisting of H, halogen, C₁-C₂₀ alkyl, C₃-C₈cycloalkyl, C(═O)R¹⁵, C(═O)NR¹⁶R¹⁷, COCl, OH, CN, C₂-C₂₀ alkenyl,oxiranyl, glycidyl, aryl, heterocyclyl, aralkyl and aralkenyl, in any ofwhich the alkyl, alkenyl or aryl, heterocyclyl or cycloalkyl groupsthere may be from 1 to 3 substituents selected from the group consistingof hydrogen, hydroxy C₁-C₄ alkoxy, acyloxy, aryl, heterocyclyl,C(═O)R¹⁵, C(═O)NR¹⁶R¹⁷, —CR¹²R¹³Y¹, CR¹¹R¹²Y¹, oxiranyl and glycidyl;where R¹⁵ is selected from the group consisting of alkyl of from 1 to 20carbon atoms, alkoxy of from 1 to 20 carbon atoms, oligo(alkoxy) inwhich each alkoxy group has 1 to 3 carbon atoms, aryloxy andheterocyclyloxy groups any of which groups may have substituentsselected from the group consisting of optionally substituted alkoxy,oligoalkoxy, amino (including mono- and di-alkyl amino and trialkylammonium, which alkyl groups, in turn may have substiuents selected fromacyl, acyloxy, alkoxy, alkoxycarbonyl, alkenoxycarbonyl, aryl andhydroxy), and hydroxyl groups; R¹⁶ and R¹⁷ are independently selectedfrom the group consisting of H and alkyl of from 1 to 20 carbon atomswhich alkyl groups, in turn may have substiuents selected from the groupconsisting of alkoxy, acyl, acyloxy, alkoxycarbonyl, alkenoxycarbonyl,aryl and hydroxy, or R¹⁶ and R¹⁷ may be joined together to form analkanediyl group of from 2 to 5 carbon atoms, thus forming a 3- to6-membered ring; and R¹³ is selected from the group consisting of alkyl,cycloalkyl, —COR¹⁵, —CONR¹⁶R¹⁷, alkenyl, aryl, heterocyclyl, aralkyl andaralkenyl groups each substituted with a biologically activesubstituent, in any of which the alkyl, alkenyl, aryl, heterocyclyl orcycloalkyl groups may have from 1 to 3 substituents selected from thegroup consisting of hydroxy, C₁-C₄ alkoxy, acyloxy, aryl, heterocyclyl,C(═O)R¹⁵, C(═O)NR¹⁶R¹⁷, —CR¹²R¹³Y¹, CR¹¹R¹²Y¹, oxiranyl and glycidylwhere R¹⁵, R¹⁶ and R¹⁷ are groups as defined above -with thebiologically active substituent substituted on an alkyl, cycloalkyl,alkenyl, aryl or heterocyclyl group, and wherein, in the living radicalpolymerization process, the group Y¹ is removed to form a radical on thecarbon to which it is linked in the initiator compound.
 2. A processaccording to claim 1 in which the initiator is a compound of generalformula VI

where R⁴¹ and R⁴² are independently selected from the group consistingof hydrogen, C₁- C₂₀ alkyl, aryl, aralkyl, C₁-C₂₀ hydroxy-alkyl,acyloxy-C₁-C₂₀-alkyl, C₃-C₈ cycloalkyl, C₃-C₈ hydroxy-cycloalkyl andacyloxy-C₃-C₈-cycloalkyl; OR⁴³ is selected from the group consisting ofan alkoxy of from 1 to 20 carbon atoms having a biological activesubstituent, an aryloxy that is biologically active and aheterocyclyloxy that is biologically active; and Y is Y¹.
 3. A processaccording to claim 2 in which either a) R⁴¹ and R⁴² are each methyl; orb) R⁴¹ is hydrogen and R⁴² is methyl.
 4. A process according to claim 3in which R⁴³ is R⁴⁴AL- derived from R⁴⁴ALOH in which R⁴⁴ is derived froma pharmacologically or diagnostically active compound R⁴⁴AH where A is adivalent moiety selected from the group consisting of O, NR³⁵ (R³⁵ is Hor lower alkyl), COO and CONR³⁵, and L is a divalent linker.
 5. Aprocess according to claim 4 in which L is an oligo-peptide-basedlinker.
 6. A process according to claim 2 in which R⁴³ is derived from apharmaceutically or diagnostically active alcohol R⁴³OH.
 7. A processaccording to claim 6 in which R⁴³OH is a carbohydrate.
 8. A processaccording to claim 7 in which the carbohydrate is a saccharide.
 9. Aprocess according to claim 2 in which Y¹ is a halogen atom.
 10. Aprocess according to claim 1 in which a biologically active moiety is asteroid moiety.
 11. A process according to claim 10 in which the steroidis cholesterol.
 12. A process according to claim 1 in which the productpolymer has a molecular weight in the range 1000 to 100,000.
 13. Aprocess according to claim 12 in which the product polymer has amolecular weight in the range 2000 to
 50000. 14. A process according toclaim 1 in which the product polymer has a polydispersity less than 1.5.15. A process according to claim 1 in which X is an ammonium,phosphonium, or sulphonium phosphate or phosphonate ester zwitterionicgroup.
 16. A process according to claim 15 in which X is a group of thegeneral formula II

in which the moieties A³ and A⁴, which are the same or different, are—O—,—S—,—NH— or a valence bond and W ⁺is a group comprising an ammonium,phosphonium or sulphonium cationic group and a group linking the anionicand cationic moieties which is a C₁₋₁₂-alkanediyl group.
 17. A processaccording to claim 16 in which X is a group of general formula III

where the groups R⁵ are the same or different and each is hydrogen orC₁₋₄ alkyl, and m is from 1 to
 4. 18. A process according to claim 17 inwhich all the groups R⁵ are methyl.
 19. A process according to claim 16in which W⁺is selected from the group consisting of —W¹—N⁺R³ ₃, —W¹—P⁺R⁴₃, —W¹—S⁺R⁴ ₂ and —W¹-Het⁺ in which: W¹ is selected from the groupconsisting of alkanediyl of 1 or more, preferably 2-6 carbon atomsoptionally containing one or more ethylenically unsaturated double ortriple bonds, disubstituted-aryl(arylene), alkylene arylene, arylenealkylene, alkylene aryl alkylene, cycloalkanediyl, alkylene cycloalkyl,cycloalkyl alkylene and alkylene cycloalkyl alkylene, which group W¹optionally contains one or more fluorine substituents and/or one or morefunctional groups; and either the groups R³ are the same or differentand each is hydrogen or alkyl of 1 to 4 carbon atoms, preferably methyl,or aryl, such as phenyl, or two of the groups R³ together with thenitrogen atom to which they are attached form an aliphatic heterocyclicring containing from 5 to 7 atoms, or the three groups R³ together withthe nitrogen atom to which they are attached form a fused ring structurecontaining from 5 to 7 atoms in each ring, and optionally one or more ofthe groups R³ is substituted by a hydrophilic functional group; and thegroups R⁴ are the same or different and each is R³ or a group OR³, whereR³ is as defined above; or Het is an aromatic nitrogen-, phosphorus- orsulphur-containing ring.
 20. A process according to claim 1 in which Yis H₂C═CR—CO—A- in which R is hydrogen or methyl and A is O.
 21. Apolymerisation process according to claim 1 in which B is a straightchain C₂₋₆ -alkanediyl.
 22. A polymerisation process according to claim1 in which the zwitterionic monomer is2-methacryloyloxyethyl-2′-trimethylammonium ethyl phosphate inner salt.23. A polymerisation process according to claim 1 in which thepolymerisation mixture contains a non-polymerisable solvent, in anamount, in the range of 10 to 500% by weight based on the weight ofethylenically unsaturated monomer.
 24. A polymerisation processaccording to claim 1 in which the ethylenically unsaturated monomerincludes at least one comonomer, selected from anionic, cationic andnon-ionic monomers and mixtures thereof.
 25. A process according toclaim 24 in which the comonomer comprises non-ionic monomer.
 26. Apolymerisation process according to claim 1 in which the catalystcomprises a transition metal compound and a ligand, in which thetransition metal compound is capable of participating in a redox cyclewith the initiator and dormant polymer chain, and the ligand is eitherany N—, O—, P— or S— containing compound which can coordinate with thetransition metal atom in a σ-bond, or any carbon-containing compoundwhich can coordinate with the transition metal in a π-bond, such thatdirect bonds between the transition metal and growing polymer radicalsand not formed.
 27. A polymerisation process according to claim 26wherein said ligand is selected from the group consisting of: a)compounds of the formulas:R²⁰—Z—R²¹ andR²⁰—Z—(R²²—Z)_(m)—R²¹ where: R²⁰ and R²¹ are independently selected fromthe group consisting of H, C₁-C₂₀ alkyl, aryl, heterocyclyl, C₁-C₆alkoxy, C₁-C₄ dialkylamino, C(═O)R²², C(═O)R²³R²⁴ and A⁷C(═O)R²⁵, whereA⁷ may be NR²⁶ or O; R²² is alkyl of from 1 to 20 carbon atoms, aryloxyor heterocyclyloxy; R²³ and R²⁴ are independently H or alkyl of from 1to 20 carbon atoms or R²³ and R²⁴ may be joined together to form analkanediyl group of from 2 to 5 carbon atoms, thus forming a 3- to6-membered ring; R²⁵ is H, straight or branched C₁-C₂₀ alkyl or aryl andR²⁶ is hydrogen, straight or branched; C₁₋₂₀-alkyl or aryl; or R²⁰ andR²¹ may be joined to form together with Z, a saturated or unsaturatedring; Z is O, S, NR²⁷ or PR²⁷, where R²⁷ is selected from the same groupas R²⁰ and R²¹, and where Z is PR²⁷, R²⁷ can also C₁-C₂₀ alkoxy or Z maybe a bond CH₂ or a fused ring, where one or both of R²⁰ and R²³ isheterocyclyl, each R²² is independently a divalent group selected fromthe group consisting of C₁-C₈ cycloalkanediyl, C₁-C₈ cycloalkanediyl,arenediyl and heterocyclylene where the covalent bonds to each Z are atvicinal positions or R²² may be joined to one or both of R²⁰ and R²¹ toformulate a heterocyclic ring system; and m is from 1 to 6; b) CO; c)porphyrins and porphycenes, which may be substituted with from 1 to 6halogen atoms, C₁₋₆ alkyl groups, C₁₋₆-alkoxy groups, C₁₋₆alkoxycarbonyl, aryl groups, heterocyclyl groups, and C₁₋₆ alkyl groupsfurther substituted with from 1 to 3 halogens; d) compounds of theformula R²³R²⁴C(C(═O)R²⁵)₂, where R^(25 is)C₁₋₂₀ alkyl, C₁₋₂₀ alkoxy,aryloxy or heterocyclyloxy; and each of R²³ and R²⁴ is independentlyselected from the group consisting of H, halogen, C₁₋₂₀ alkyl, aryl andheterocyclyl, and R²³ and R²⁴ may be joined to form a C₁₋₈ cycloalkylring or a hydrogenated aromatic or heterocyclic ring, of which the ringatoms may be further substituted with 1 to 5 C₁₋₆ alkyl groups, C₁₋₆alkoxy groups, halogen atoms, aryl groups, or combinations thereof; ande) arenes and cyclopentadienyl ligands, where said cyclopentadienylligand may be substituted with from one to five methyl groups, or may belinked through and ethylene or propylene chain to a secondcyclopentadienyl ligand.
 28. A polymerisation process according to claim27 in which the ligand is selected from the group consisting ofbipyridine, triphenylphosphine, 1,1,4,7,10,10-hexamethyl-triethylenetetramine, or a compound of the general formula VII

where R⁴⁰ is an alkyl or substituted alkyl group, in which thesubstituent is selected from amino, including alkylamino and acylamino,alkoxy, hydroxy, acyl, acyloxy, alkoxycarbonyl, heterocyclyl, ionicgroups and halogen.
 29. A polymerisation process according to claim 26in which the transition metal compound has the formula M_(t)^(n+)X′_(n), where: M_(t) ^(n+)may be selected from the group consistingof Cu¹⁺, Cu²⁺, Fe²⁺, Fe³⁺, Ru²⁺, Ru³⁺,Cr²⁺, Cr³⁺, Mo²⁺, Mo³⁺, W²⁺, W³⁺,Mn²⁺, Mn³⁺, Mn⁴⁺, Rh³⁺, Rh⁴⁺, Re²⁺, Re³⁺, Co⁺, Co²⁺, Co³⁺, V²⁺, V³⁺,Zn⁺, Zn²⁺, Ni²⁺, Ni³⁺, Au⁺, Au²⁺, Ag⁺, and Ag²⁺; X′ is selected from thegroup consisting of halogen, C₁₂-C₆-alkoxy, (SO₄)_(1/2), (PO₄)_(1/3),(R¹⁸PO₄)½(R¹⁸ ₂PO₄) triflate, hexafluorophosphate, methanesulphonate,arylsulphonate, CN and R¹⁹CO₂, where R¹⁸ is aryl or a straight orbranched C₁₋₂₀ alkyl and R¹⁹ is H or a straight or branched C₁-C₆ alkylgroup which may be substituted from 1 to 5 times with a halogen; and nis the formal charge on the metal (0≦n≦7).
 30. A polymerisation processaccording to claim 29 in which the metal compound is CuHal or RuHal₂where Hal is chlorine or bromine.